What characteristic should a rivet set have when driving MS20470 rivets?

The characteristic that a rivet set should have when driving MS20470 rivets is a slightly greater radius than the rivet head. This design ensures that the rivet set properly engages with the rivet head during the riveting process, allowing for effective deformation of the rivet without being excessively large.

A slightly larger radius facilitates better contact, which helps distribute the force applied during the riveting process evenly across the head. This reduces the risk of damage to the rivet head while still ensuring that sufficient force is applied to create a proper mechanical bond when the rivet is deformed. Furthermore, using this radius helps prevent issues such as slippage or misalignment, which can occur if the rivet set's radius is the same as or smaller than the rivet head.

By having a radius just slightly greater, the set can efficiently form the rivet and achieve a solid joint, vital for the integrity of an airframe structure. The other options do not support the best practice in riveting, such as proper rivet deformation and head protection.